2003 Protege ES 2.0 Battery light possessed

[pittstang5]

Need some help here.

Mazda Protege ES 2.0L 2003

I'll be driving, usually coming to a stop and the battery light will come on randomly. I've noticed it at lower RPMs (Idle to about 1500 rpms) then going away at higher RPMS (Usually goes off between 1500 - 2000 or higher). The light hasn't stayed on long enough for me to get an actual voltge reading when this occurs because as soon as I am anywhere near a voltage meter, the light goes off and everything checks out ok. Finally today, it happened again and I had a volt meter in the car with me. Voltage read 11.9 at idle. So I close the hood and figure I better get my butt home before this thing dies. Here's the wierd thing. Tempting fate, I decided to experiment. I was just running the heater in the car (vent) and radio - everything was still working fine. I turn on the defroster full blast, the idle picked up a hair and the battery light goes off. (No I didn't go back under the hood and check the voltage - at this point I just wanted to get home) I ran with the defroster on for a couple miles and switch back to the vent - still no light. Got home with no light. Now why would the light go off when the defroster came on? Is there something wrong with my idle that would cause this or is it the alternator or is it the alternator belt. I would think it's the alternator, but don't those things "work" or "don't work."

It just started doing this randomly for at least the last two months - maybe longer. Definitely started noticing this since it got cold out.

Side question - how do you tightened the alternator belt? Is it that long bolt on top of the alternator that looks like it's in a bracket?

Thanks for the help.

 

[concept]

Is the alternator belt loose? If so, I would tighten it. That could be your problem, although typically, the belt will squeal when you start your car in the morning/when the engine is cold. I can't look at my car right now, but look at the assembly, carefully. It should be somewhat obvious. If the belt is tight, you can have your alternator tested.

Having the defroster on will speed up engine rpm, which explains why the light turned off. I'll bet your battery needs a charge.

 

[MikeyP1990]

11.9v while at idle makes me think that your alternator is to blame. maybe it's putting out enough juice at the upper RPMs but not at the lower. quite possible. swing by an autozone and have them test it while its in the car.